In a conventional epitaxial growth system, reaction gases are supplied to a reaction chamber, and a semiconductor wafer is heated to thermally decompose the supplied gases, thereby growing a thin film having a predetermined composition on the wafer. Products and non-reacted gases which are not used for growing the thin film on the wafer are exhausted from the reaction chamber through an exhaust pipe. In general, such an exhaust pipe is coupled with a pressure control valve that is configured to control a pressure value inside the reaction chamber. Typically, it is not uncommon to see that the unreacted/excessive gases from the chamber may form a solid phase by-product along the pipe and/or over the pressure control valve. Thus, a need to avoid such by-products being formed in an exhaust system, especially over the pressure control valve, is desired.